Generally, ophthalmic lenses have two opposing refracting surfaces and are worn adjacent the eye in a spectacle frame to assist the function of the eye. In one existing method of manufacturing ophthalmic lenses for a lens wearer, semi-finished ophthalmic lenses are first produced with a finished surface on one side only by a lens manufacturer. The surface on the other side of the semi-finished ophthalmic lens is subsequently finished by, for instance, further grinding and polishing to fit a lens wearer's prescription at a prescription (Rx) laboratory and form finished ophthalmic lenses. It will be appreciated by a person skilled in the art that the lens wearer's ophthalmic prescription (Rx script) is a formula determined by an examiner to correct anomalies in a lens wearer's sight, usually including sphere, cylinder, addition and prism powers as well as decentration.
With respect to the above described existing semi-finished ophthalmic lenses, in an example, an Rx laboratory receives prescription data of a lens wearer (e.g. sphere, cylinder, addition and prism power data) from an examiner and selects one of a set of semi-finished ophthalmic lenses for further grinding and polishing to produce a lens that fits the lens wearer's prescription. The set of semi-finished ophthalmic lenses is made from a designated lens material with a designated refractive index (e.g. 1.67) and each of the lenses has a determined geometry including one of a plurality of base curves determined to allow manufacture of the finished ophthalmic lenses for substantially all ophthalmic lens prescriptions. The base curves, on semi-finished ophthalmic lenses, provide surface power for the first side curve (e.g. front) which, when combined with the second side curve (e.g. back, facing a wearer's eye), after it is ground and polished, produces the desired lens power. It will be appreciated by those persons skilled in the art that the first and/or second side curves can be spherical, aspherical and/or progressive surfaces. It will also be appreciated that the determined geometries of the lenses in the set differ with different designated refractive indexes; for example, lenses with a refractive index of 1.67 are thinner than those with a refractive index of 1.6. It will also be appreciated that a base curve is a surface power of the finished surface of a semi-finished lens which, when combined with the eventually finished other surface of the lens, forms the desired lens power. Thus, for example, a lens manufacturer produces a set of, say, thirteen semi-finished ophthalmic lenses—each of the lenses having different base curves—for Rx laboratories to form finished lenses for substantially all possible prescriptions. Accordingly, each of the semi-finished lenses in the set—sometimes called blanks or pucks in the art, particularly for “Freeform” usage—must be able to satisfy a subset of wearer and/or frame data to produce suitable finished lenses. “Freeform” refers to a lens manufacturing process that can create most curve configurations from a semi-finished ophthalmic lens by cutting the semi-finished ophthalmic lens in a specified manner. It will be appreciated by a person skilled in the art that the “Freeform” process is more sophisticated than traditional lens manufacturing processes and, for example, employs a cutting point controlled by a CNC machine to cut a lens rather than traditionally grinding the lens. As a result, the “Freeform” process is able to produce much more complex surfaces that include, but not limited to, sphere, cylinder and addition powers combined together. It will be appreciated that the complexity of a lens surface relates to its manufacturing difficulty.
As described, the geometries of each of the lenses in the existing exemplary set of semi-finished ophthalmic lenses are determined to allow for an extensive range of ophthalmic lens prescriptions to be assigned to each base curve produced (e.g. usually not exceed 6 Dioptres of Cylinder). It will be appreciated that the geometry of a lens includes its diameter and thickness. Thus, each lens in the set is designed to have a geometry that is large enough in thickness and diameter to allow for manufacture of substantially all prescriptions that are assigned to each of the base curves. Accordingly, thick and large diameter semi-finished lenses are produced to suit all prescriptions and frame sizes which include some rare prescriptions that lie far outside the norm for common prescriptions. Accordingly, for common prescriptions that do not require such a thick and large semi-finished lens, there is significant lens material wastage. It will be appreciated that extreme outlier Rx scripts—clinical rarities—are manufactured as special cases using very large bespoke puck components, and are not considered part of the “standard range population”; that is, substantially all ophthalmic lens prescriptions.
It is therefore an aim of the present invention to provide a method of optimising geometry of at least one semi-finished ophthalmic lens in a set of semi-finished ophthalmic lenses to, for instance, minimise lens material wastage.
Before turning to a summary of the present invention, it will be appreciated that the discussion of the background to the invention is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge in Australia or in any other country.